This invention relates to the forming of miniature mold cavities for molding small features integral with a base sheet, and has particular application to the production of touch fasteners and the like.
Touch fastener products have arrays of miniature fastener elements (for instance, hook-shaped or mushroom-shaped elements) extending from a common base. Typically, in order to be capable of engaging a loop fiber or another fastener element, these fastener elements have overhanging xe2x80x9ccrooksxe2x80x9d, such as the hook portion of a hook-shaped element or the underside of the head of a mushroom-shaped element. These crooks snag and retain loop fibers, for instance, to form a fastening, but can be challenging to mold in their fully functional form in non-opening mold cavities.
One solution for continuously molding such fastener elements for touch fasteners and other products was disclosed by Filcher in U.S. Pat. No. 4,794,028. In commercial implementations of his solution, a cylindrical, rotating mold roll is composed of a large number (e.g., thousands) of thin, disk-shaped mold plates and spacer plates which are stacked concentrically about a central barrel. Extending inwardly from the periphery of the mold plates are cavities for molding the hook elements. These mold cavities are composed of contoured mold surfaces in the mold plates in combination with flat side surfaces of adjoining spacer plates. To produce mold plates for current production machines, each contoured mold surface is typically formed by electro-discharge machining (EDM) methods.
We have realized that extremely small mold cavity surfaces can be accurately formed at reasonable cost by controllably building up mold material in patterned layers, such as by plating techniques.
The invention features a method of producing a multiplicity of cavities extending from a common surface, for molding a plastic product having a multiplicity of features integrally molded with and extending from a product base. The method includes depositing multiple layers of plating material on a workpiece in a predetermined pattern selected to produce a desired mold cavity shape, and forming, with the plating material, mold surfaces for defining a multiplicity of feature-shaped mold cavities extending from a common surface.
In some cases, the cavities each have a crook for molding a fastener element, such as a hook-shaped fastener element, with an engageable crook portion.
Preferably, the cavities are constructed to mold features of less than about 0.050 inch in total height, more preferably less than about 0.025 inch in total height, as measured from the product base.
The workpiece can, for instance, comprise at least part of a mold for molding a plastic fastener product.
The method can include the steps of applying a masking material to selected portions of the workpiece to produce masked surfaces, depositing a layer of the plating material to the workpiece to surfaces other than the masked surfaces, and removing the masking material from the masked surfaces to expose unplated surfaces of the workpiece.
In some cases the workpiece comprises a flat plate, the plating material being deposited on one broad side of the plate to form mold surfaces at an edge thereof, for defining mold cavities extending from the edge. The plating material can be deposited to form one side of a mold cavity, another side of the cavity being defined by a surface of an adjoining plate. The deposited plating material can be machined to remove an outer portion thereof to provide a flat surface for abutting an adjoining mold part.
The plating material, in some embodiments, defines fully-formed mold cavities, each extending from an innermost portion to a base portion at an outer surface of the plating, the layers of deposited plating material defining, in order of deposition, the cavities from their innermost portions to their base portions. The workpiece can comprise a flexible belt.
The overall thickness of the multiple layers of plating material is preferably between about 0.001 inch and 0.015 inch, more preferably between about 0.002 inch and 0.007 inch, even more preferably about 0.004 inch.
In some embodiments the workpiece comprises a master, the method further comprising the step of removing the master from the plating to form a mold for molding a plastic fastener product. The master can have fastener elements, such as hook-shaped fastener elements, extending from a surface of the product base. Sometimes the method includes depositing a layer of metal, such as copper, on the master before depositing the plating material.
The mold can include a cylindrical mold sleeve with fully-formed mold cavities extending inward from its outer surface.
Preferably the mold has an overall thickness of between about 0.005 inch and 0.050 inch.
The invention also features a method of producing a multiplicity of cavities extending from a common surface of a mold, for molding a fastener product having an array of fastener elements integrally molded with and extending from a product base. The method comprises depositing multiple layers of plating material on a workpiece in a predetermined pattern selected to produce desired mold cavity shapes, including building up the plating material to a sufficient thickness to encompass and form mold surfaces within the thickness of the plating.
According to another aspect of the invention, a mold is provided for molding a plastic product having features integrally molded with and extending from a product base. The mold includes a stratum of mold material having an outer surface and composed of multiple layers of plating material deposited in a predetermined pattern. The stratum of mold material defines therewith in a multiplicity of mold surfaces comprising the plating material in an as-deposited state. The mold surfaces are arranged to form mold cavities extending inwardly from the outer surface of the stratum of mold material for molding an array of features integral with a base formed by the outer surface of the stratum. The mold is preferably constructed to mold a fastener element with an engageable crook portion.
The stratum of mold material is preferably between about 0.001 inch and 0.015 inch.
The mold can be constructed to rotate to continuously produce a product in strip form, and can be in the form of a mold roll or a mold belt, for instance.
In some embodiments, the mold includes a flat plate, the plating material being disposed on one broad side of the plate to form mold surfaces at an edge thereof for defining mold cavities extending from the edge. The mold can include a multiplicity of such flat plates stacked together along a common axis.
In some cases the mold roll is composed of a cylindrical mold sleeve with fully-formed mold cavities extending inwardly from its outer surface. The mold sleeve preferably has an overall thickness of between about 0.005 inch and 0.050 inch, and can have an outermost layer containing copper.
By xe2x80x9cplating materialxe2x80x9d we mean metal-containing material that is deposited as a thin, free-form layer upon a surface, such as by electroplating, electroless plating, sputtering or vapor deposition, for examples.
Molds produced according to the invention can be very cost-effective, as multitudes of very accurate and extremely small mold surfaces can be simultaneously formed without precise machining of each individual mold surface. Molds with fully-formed mold cavities enclosed and defined by multiple layers of plating material can be readily produced in thin, semi-disposable sleeve or belt form, easily replaced and providing high rates of heat transfer from the mold cavities, thus enabling high production speeds.
These and other advantages and features will be understood from the following description, drawings and claims.